Daylight collection systems and methods

ABSTRACT

Lighting devices and methods for illuminating the interior of a building with natural daylight are disclosed. In some embodiments, a daylighting apparatus includes a tube having a sidewall with a reflective interior surface, an at least partially transparent light collector with one or more light turning elements, and a light reflector positioned to reflect daylight into the light collector. The one or more light turning elements can turn direct and indirect daylight into the tube so that it is available to illuminate the building. In some embodiments, the tube is disposed between the light collector and a diffuser positioned inside a target area of a building. In certain embodiments, the tube is configured to direct at least a portion of the daylight transmitted through the light collector towards the diffuser.

RELATED APPLICATION Incorporation by Reference to Any PriorityApplications

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are incorporated by reference under 37 CFR 1.57 and made apart of this specification.

BACKGROUND

1. Field

This disclosure relates generally to light collectors and lightcollection methods used in daylighting.

2. Description of Related Art

Daylighting systems typically include windows, openings, and/or surfacesthat provide natural light to the interior of a building. Examples ofdaylighting systems include skylights and tubular daylighting device(TDD) installations. In a TDD installation, a transparent cover can bemounted on a roof of a building or in another suitable location. TDDscan have various configurations. For example, an internally reflectivetube can connect the cover to a diffuser mounted in a room or area to beilluminated. Natural light entering the cover on the roof can propagatethrough the tube and reach the diffuser, which disperses the naturallight throughout a room or area inside of the building. Various devicesand methods exist for receiving daylight into a TDD. Certain currentlyknown devices and methods for receiving daylight into a TDD suffer fromvarious drawbacks.

SUMMARY

Lighting devices and methods for illuminating the interior of a buildingwith natural daylight are disclosed. In some embodiments, a daylightingapparatus includes a tube having a sidewall with a reflective interiorsurface, an at least partially transparent light collector with one ormore light turning elements, and a light reflector positioned to reflectdaylight into the light collector. The one or more light turningelements can turn direct and indirect daylight into the tube so that itis available to illuminate the building. In some embodiments, the tubeis disposed between the light collector and a diffuser positioned insidea target area of a building. In certain embodiments, the tube isconfigured to direct at least a portion of the daylight transmittedthrough the light collector towards the diffuser.

Some embodiments disclosed herein include lighting devices and methodsthat collect a large quantity of natural light substantially throughoutthe daytime hours of generally sunny days. An exterior daylightcollector can direct the natural light into a light guide that isdisposed between the daylight collector and a diffuser or light aperturelocated inside of a building. The light guide can direct the naturallight to the diffuser or aperture, and the natural light can provide asubstantial amount of illumination to the interior of the building.

In some embodiments, a tubular daylighting device includes a lightcollector, a generally vertical reflective tube extending from thegeneral area of the light collector, and a diffuser disposed at theopposite end or region of the reflective tube. The light collectorpermits exterior light, such as natural light, to enter the interior ofthe reflective tube. The tube guides the exterior light down to thediffuser, which disperses the light generally throughout a target roomor area in the interior of a building. The light collector can have oneor more components. For example, the light collector can include atransparent top cover, a prismatic top cover, other prismatic elements,one or more light turning assemblies, a durable cover, one or morereflective surfaces (e.g., positioned inside or outside of thecollector), other optical elements, other components, or a combinationof components. At least some components of the light collector can beconfigured to be positioned on the roof of a building or in anothersuitable area outside of the building.

In some embodiments, a daylighting apparatus is configured to directnatural daylight into an interior of a building. The apparatus caninclude an at least partially transparent light-collecting assemblycomprising a substantially vertical sidewall portion and a horizontalcollector base aperture; a reflector positioned and configured toreflect natural daylight towards the substantially vertical sidewallportion; and a light turning assembly positioned and configured to turnlight transmitted through the at least partially transparentlight-collecting assembly towards the collector base aperture. Thedaylighting apparatus can be configured to provide natural illuminationto the interior of the building when the daylighting apparatus isinstalled on a roof of the building and when the daylighting aperture isaligned with an opening formed in a roof of the building.

The reflector can be curved in one or more dimensions, can be planar, orcan have a combination of curved and/or planar sections. The reflectorcan have a plurality of segments. The reflector can be supported by oneor more support legs configured to raise a lower edge of the reflector asubstantial distance above a roof of the building when the reflector isinstalled on the building.

In some embodiments, the reflector includes one or more optical elementsconfigured to alter an angle of reflection of at least a portion of thelight that strikes the reflector. The one or more optical elements caninclude a prismatic element, such as a prismatic film. The reflector caninclude a first portion having a first prismatic element, and a secondportion having a second prismatic element. The first prismatic elementand second prismatic element can have different light-turningcharacteristics.

In certain embodiments, the reflector is configured to tilt forwardand/or backward. The reflector can be substantially parabolically-shapedalong at least one axis of curvature. The reflector can be positionedsuch that a cross-sectional center of the light-collecting assembly ispositioned at a focus point of the reflector.

In some embodiments, the reflector is configured to rotate about a firstaxis of rotation. The first axis of rotation can be locatedsubstantially at the center of the light-collecting assembly. Thereflector can also be configured to rotate about at least a second axisof rotation. The reflector can be configured to automatically rotate tosubstantially track a solar azimuth angle. The tracking system canrotate the reflector such that it tracks the solar azimuth angle within5° or within another suitable tolerance.

The light turning assembly of a daylighting apparatus can include aprismatic element, a reflective element, another optical element, or acombination of optical elements. In some embodiments, thelight-collecting assembly includes a vertical portion and a top coverportion. At least one of the vertical portion or the top cover portioncan include a prismatic element. For example, a prismatic film can bedisposed within the vertical portion of the light-collecting assembly.The top cover portion can include a plurality of segments, each of whichhas a different outside surface angle, or can include a single exteriorsegment having a substantially unvarying slope. The top cover portioncan include a single exterior segment having a substantially varyingslope.

Certain embodiments provide a method of directing natural daylight intoan interior of a building. The method can include positioning areflector outside of a light-collecting apparatus disposed over ahorizontal daylighting aperture formed in a building envelope andreflecting natural daylight using the reflector towards a substantiallyvertical sidewall of the light-collecting apparatus. The substantiallyvertical sidewall can be at least partially transparent. The method caninclude transmitting the reflected natural daylight through thesubstantially vertical sidewall of the light-collecting apparatus andturning the reflected natural daylight towards the daylighting aperturesuch that a substantial portion of the reflected natural daylight isavailable for illuminating the interior of the building.

In some embodiments, the method can include automatically repositioningthe reflector such that an apex of the reflector generally tracks asolar azimuth angle during daylight hours.

In certain embodiments, a daylighting apparatus is configured to providenatural light to the interior of a building. The apparatus can include atransparent light-collecting assembly and a reflector configured toreflect natural light towards the light-collecting assembly. Thereflector can be substantially parabolically-shaped and include at leasta vertex portion.

Some embodiments provide a method of providing light to an interior of abuilding. The method can include positioning a reflector outside of alight-collecting apparatus positioned over a daylighting aperture formedin a building envelope. The reflector can be substantiallyparabolically-shaped and include at least a vertex portion. The methodcan include reflecting natural daylight using the reflector towards thelight-collecting apparatus; transmitting the reflected natural daylightthrough a transparent sidewall of the light-collecting apparatus; andturning the reflected natural daylight towards the daylighting aperturesuch that a substantial portion of the reflected natural daylight isavailable for illuminating the interior of the building. In certainembodiments, the method includes moving the reflector to track a solarazimuth angle.

In certain embodiments, a daylighting apparatus is configured to providenatural daylight to the interior of a building. The apparatus caninclude a daylight collector defining a daylighting aperture configuredto be positioned substantially horizontally or substantially parallel toa plane of a roof of the building surface when the daylighting apparatusis installed on the building; a reflector having a substantiallyparabolic shape, the reflector configured to reflect daylight such thata substantial portion of reflected daylight is directed towards thedaylight collector; and a light turning optical element configured toturn reflected daylight transmitted through the daylight collectortowards the daylighting aperture.

The daylighting apparatus can include a tracking system configured toturn the reflector such that an apex of the reflector generally tracks asolar azimuth angle during daylight hours. The reflector can beconfigured to reflect daylight into the daylighting aperture such thatreflected daylight is directed through a surface extending upwardly fromat least half of a perimeter of the daylighting aperture. The surfacecan extend upwardly from at least about 58% of the perimeter of thedaylighting aperture. The reflector can have a luminous reflectancegreater than or equal to about 99% when measured with respect to CIEIlluminant D₆₅. The light turning optical element can include aprismatic film positioned to refract light passing through the daylightcollector. The light turning optical element can include a reflectorpositioned to reflect light passing through the daylight collector.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments are depicted in the accompanying drawings forillustrative purposes, and should in no way be interpreted as limitingthe scope of the inventions. In addition, various features of differentdisclosed embodiments can be combined to form additional embodiments,which are part of this disclosure. Any feature or element can be removedor omitted. Throughout the drawings, reference numbers may be reused toindicate correspondence between reference elements.

FIG. 1 is a cross-sectional view of a TDD installation.

FIG. 2 is a perspective view of a dome-shaped light collector.

FIG. 3 is a cross-sectional view of a dome-shaped light collector.

FIG. 4 is a partial cross-sectional view of the dome-shaped lightcollector of FIG. 3 having a prismatic element.

FIG. 5 is another partial cross-sectional view of the dome-shaped lightcollector of FIG. 3 having a prismatic element.

FIG. 6 is a cross-sectional view of a light-collecting assembly havingvertical and top cover portions.

FIG. 7 is a cross-sectional view of a light-collecting top coverportion.

FIG. 8 is a cross-sectional view of a light-collecting vertical portion.

FIG. 9 is a cross-sectional view of a light collector.

FIG. 10 is a top view of the light collector of FIG. 9.

FIG. 11 is a perspective view of a light collector.

FIG. 12 is a perspective view of a light collection system comprising areflector.

FIG. 13 is a top view of a light collection system comprising aparabolic reflector.

FIG. 14 is a cross-sectional view of a TDD installation.

FIG. 15 is a cross-sectional view of a light collection systemcomprising a reflector.

FIG. 16 is a cross-sectional view of a light reflector.

FIG. 17 is a cross-sectional view of a light reflector.

FIG. 18 is a perspective view of a light collection system comprising aplanar reflector.

FIG. 19 is a perspective view of a light collection system comprising areflector having a plurality of panels.

FIG. 20 is a perspective view of a light collection system comprising areflector having raised peripheral portions.

FIG. 21 is a cross sectional view of a light reflector.

FIG. 22 is a perspective view of a TDD installation.

FIG. 23 is an exploded view of a light collection system comprising areflector and a prismatic film.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Although certain preferred embodiments and examples are disclosedherein, inventive subject matter extends beyond the examples in thespecifically disclosed embodiments to other alternative embodimentsand/or uses, and to modifications and equivalents thereof. Thus, thescope of the claims appended hereto is not limited by any of theparticular embodiments described below. For example, in any method orprocess disclosed herein, the acts or operations of the method orprocess may be performed in any suitable sequence and are notnecessarily limited to any particular disclosed sequence. Variousoperations may be described as multiple discrete operations in a manneror order that may be helpful in understanding certain embodiments;however, the order of description should not be construed to imply thatthese operations are order-dependent. Additionally, the assemblies,systems, and/or devices described herein may be embodied as integratedcomponents or as separate components. For purposes of comparing variousembodiments, certain aspects and advantages of these embodiments aredescribed. Not necessarily all such aspects or advantages are achievedby any particular embodiment. Thus, for example, various embodiments maybe carried out in a manner that achieves or optimizes one advantage orgroup of advantages as taught herein without necessarily achieving otheraspects or advantages as may also be taught or suggested herein.

In some embodiments, tubular daylighting devices include a lightcollector, a generally vertical reflective tube extending from thegeneral area of the light collector, and a diffuser disposed at theopposite end or region of the reflective tube. The light collectorpermits exterior light, such as natural light, to enter the interior ofthe reflective tube. The tube guides the exterior light down to thediffuser, which disperses the light generally throughout a target roomor area in the interior of a building. The light collector can have oneor more components. For example, the light collector can include atransparent dome, a prismatic dome, other prismatic elements, one ormore light turning assemblies, a durable cover, one or more reflectivesurfaces (e.g., positioned inside or outside of the collector), otheroptical elements, other components, or a combination of components. Atleast some components of the light collector can be configured to bepositioned on the roof of a building or in another suitable area outsidethe building.

A daylighting device can include an optical collimator configured toturn light propagating through the daylighting device such that, whenlight (such as, for example, daylight, auxiliary light, or daylight andauxiliary light) exits the daylighting device and/or enters a diffuser,the light has increased alignment, as compared to a device without acollimator. In some embodiments, a substantial portion of lightpropagating through a daylighting device may propagate within thedaylighting device at relatively low angles of elevation from ahorizontal plane of reference. Such angles of propagation may, in somesituations, cause the light to have undesirable properties when it exitsthe daylighting device. For example, the optical efficiency of adiffuser substantially positioned within a horizontal plane can besubstantially reduced when light is incident on the diffuser at lowangles of elevation from the horizontal plane. As another example, lightthat is incident on the diffuser at low angles of elevation can resultin light exiting the daylighting device at an exit angle of greater thanor equal to about 45 degrees from vertical. Light exiting a daylightingdevice at those angles can create glare and visibility issues in thearea or room being illuminated.

A collimator apparatus can be configured such that light that wouldotherwise enter the diffuser at undesirable angles is turned to a moredesirable angle. For example, the collimator or light aligning apparatuscan ensure that light passing through the daylighting device will exitthe daylighting device at an exit angle of less than or equal to about45 degrees from vertical, or at a substantially or nearly verticalorientation, when the diffuser is horizontal. In some embodiments, thecollimator or light aligning apparatus can ensure that light passingthrough the daylighting device will exit the daylighting device at anexit angle of less than or equal to about 45 degrees from a longitudinalaxis of the daylighting device or a portion of the daylighting device,or at an orientation substantially or nearly parallel to thelongitudinal axis of the daylighting device or a portion of thedaylighting device. In certain embodiments, the collimator apparatus isconfigured to reduce or prevent the light from exiting the daylightingdevice at an angle of between about 45 degrees and about 60 degrees fromvertical. In this manner, the collimator apparatus can reduce oreliminate the glare and visibility issues that light exiting a lightingfixture between those angles can cause.

The daylighting device can include an auxiliary lighting system. Forexample, the auxiliary lighting system can be inserted into the tube toprovide light from the tube to a target area or room when sunlight isnot available in sufficient quantity to provide a desired level ofinterior lighting. In some embodiments, tubular daylighting devices inwhich the lighting fixture is suspended from a rod or wire may sufferfrom various drawbacks. For example, the rod, or other apparatus forsupporting the lamp, and the lamp itself may occupy a substantialportion of the tube interior, thereby reducing the performance of thetubular daylighting device. If a lighting apparatus is attached to afixture such as a rod or wire in the center of the tube, and especiallyif the lighting apparatus has a heat exchanger attached to its backside, a large amount of daylight can be blocked from continuing down thetube.

In some cases, a lighting apparatus typically illuminates in a patternthat allows nearly half of the generated light to be lost back up thetube. Moreover, in some cases, only a portion of the light from the lampenters the tube base diffuser at an incident angle that provides hightransmission efficiencies. When the incident angle of light on thediffuser is high, a greater portion of light can be reflected back upthe tube by the diffuser. This effect, together with the light lost upthe tube due to the illumination pattern of the lamp, can result in asubstantial portion of light from the lamp not reaching the targetedarea. Also, in some cases, if the lighting apparatus is facing towardsthe diffuser, it can create a very bright spot of light that may requirefurther diffusion to eliminate glare and reduce contrast.

Some daylighting devices and methods can incorporate an auxiliarylighting system that is connected to, or used in connection with, acollimator to achieve desirable illumination properties. In someembodiments, the collimator is configured to increase the collimation ofboth natural light and light emanating from one or more auxiliary lightsources. Certain embodiments are configured to provide a desirabledistribution and level of illumination within a target area or roomunder a wide range of natural light conditions. Examples of providing adesirable distribution and level of illumination include providing asubstantially even distribution of interior light using any combinationof natural light and artificial light, providing a substantially steadylevel of illumination during daytime or nighttime, providing adistribution of interior light that does not change substantiallybetween daytime and nighttime, providing at least a threshold level ofillumination, or any combination of such features.

In some embodiments, a daylighting device is configured to providegreater than or equal to about 400 lumens, greater than or equal toabout 450 lumens, greater than or equal to about 500 lumens, greaterthan or equal to about 1000 lumens, greater than or equal to about 2000lumens, greater than or equal to about 3000 lumens, or another suitablelevel of illumination during daytime or nighttime. In certainembodiments, a daylighting device is configured to provide directillumination of surfaces substantially throughout a room of greater thanor equal to about 1 lumen, 2 lumens, 3 lumens, 4 lumens, or 5 lumens persquare foot, greater than or equal to about 1 lumen per square footand/or less than or equal to about 15 lumens per square foot, betweenabout 1 lumen and about 10 lumens per square foot, between about 3lumens and about 10 lumens per square foot, or within another suitablerange. In some embodiments, a daylighting device is configured toprovide illumination such that the difference between the greatest levelof illumination and the least level of illumination of surfaces thatreceive direct illumination from the daylighting device is less than orequal to a threshold level. In certain embodiments, the threshold levelof differing illumination level for directly illuminated surfaces isabout 5 lumens, 4 lumens, 3 lumens, 2 lumens, or 1 lumen per squarefoot.

The term “collimator” is used herein according to its broad and ordinarysense, and includes, for example, light-aligning assemblies having oneor more sidewalls with a reflective interior surface configured suchthat the exit angle of the light reflected by the collimator is closerto parallel to a longitudinal axis of the tube (e.g., closer tovertical) than the entrance angle of the light. In some embodiments, acollimator increases the elevation angle from a reference planeperpendicular to a longitudinal axis of the tube (e.g., from horizontal)of at least a portion of the light propagating through the daylightingdevice such that the at least a portion of the light exits thedaylighting device at a more vertical angle. The degree to which thelight is turned can depend on the orientation and position of theportion of the one or more reflective interior surfaces on which thelight is incident.

Some embodiments disclosed herein provide a daylighting apparatusincluding a tube having a sidewall with a reflective interior surface, acollimating assembly, and an auxiliary light fixture. The tube can bedisposed between a transparent cover positioned to receive daylight anda diffuser positioned inside a target area of a building. In certainembodiments, the tube is configured to direct the daylight transmittedthrough the transparent cover towards the diffuser. The auxiliary lightfixture can include a lamp disposed within the tube and a light controlsurface configured to reflect light exiting the lamp towards thediffuser and to transmit daylight propagating through the tube from thedirection of the transparent cover. The lamp can be disposed on theinterior sidewall of the tube or otherwise positioned in a way thatpermits light generated by the lamp to pass into the interior of thetube.

As used herein, “tube” is used in its broad and ordinary sense. Forexample, a tube includes any conduit, channel, duct, guide, chamber,pipe, pathway or passageway, regardless of cross-sectional shape orconfiguration, and such terms may be used interchangeably, whereappropriate. For example, a tube may be generally cylindrical in shape,or may have a rectangular, oval, triangular, circular, or anothercross-sectional shape or combination of cross-sectional shapes.Furthermore, references to tubes or tubular assemblies may refer toassemblies having any suitable length, width or height.

FIG. 1 shows a cross-sectional view of an example of a tubulardaylighting device 10 installed in a building for illuminating, withnatural light, an interior room 12 of a building. Certain embodiments ofdaylighting devices disclosed herein may be particularly suited for highbay applications. For example, daylighting devices as described hereinmay be suited for installation in buildings with an interior ceilingapproximately 20 feet high, or higher. The tubular daylighting device 10includes a transparent light collector 20 mounted on a roof 18 of thebuilding that allows natural light to enter a tube 24. The lightcollector 20 can be mounted to the roof 18 using a flashing 22. Theflashing 22 can include a flange 22 a that is attached to the roof 18,and a curb 22 b that rises upwardly from the flange 22 a and may beangled as appropriate for the cant of the roof 18 to engage and hold thelight collector 20 in a generally vertically upright orientation. Theroof 18 and/or ceiling 14 may be supported by one or more joists 15.

In certain embodiments, the light collector 20 is at least partiallytransparent and may be made of any suitable material, e.g., acrylic,polycarbonate, plastic, glass, etc. The light collector 20 may includeone or more optical elements for bending, turning, converging,diverging, or otherwise altering the path of light entering the lightcollector.

The tube 24 can be configured in a generally vertical orientation,spanning the area between the roof 18 and the ceiling 14 of the interiorof room 12. In certain embodiments, the tube 24 is connected to theflashing 22. The tube 24 can direct light that enters the tube 24generally downwardly to a light diffuser 26, which disperses the lightin the room 12. The tube 24 can be made of metal, fiber, plastic, arigid material, an alloy, another appropriate material, or a combinationof materials. For example, the body of the tube 24 can be constructedfrom type 1150 alloy aluminum. The interior of the tube 24 may bereflective. For example, the interior of the tube 24 may be renderedreflective by means of, e.g., electroplating, anodizing, metalizedplastic film coating, or other suitable means. In certain embodiments,the tube assembly 24 is rendered internally reflective by laminating theinside surface of the tube assembly with a multi-ply polymericdaylighting film made by the 3M Company of Maplewood, Minn., USA. Othersuitable reflective materials can be used to cause the interior surfaceof the tube 24 to be highly reflective of visible light.

The tube 24 can terminate at a light diffuser 26. The light diffuser 26can include one or more devices that spread out or scatter light in asuitable manner. In some embodiments, the diffuser 26 absorbs relativelylittle or no visible light and transmits most or all incident visiblelight, at least at certain angles of incidence. The diffuser can includeone or more lenses, ground glass, holographic diffusers, or any othersuitable diffusers. The diffuser 26 can be connected to the tube 24using any suitable connection technique. For example, a seal ring can besurroundingly engaged with the tube 24 and connected to the lightdiffuser 26 to hold the diffuser 26 onto the end of the tube 24.

The amount of light that enters the tube 24 through the light collector20 may at least partly depend on the effective area of the tube aperturewith respect to the suns radiation, as well as the intensity of thesunlight. Both of these parameters may be substantially reduced in theearly morning and/or late afternoon relative to mid-day levels. Withrespect to certain TDD embodiments, this may result in substantialvariations of interior illumination throughout the day, which mayrequire supplemental lighting in the morning/evening and/or shading atcertain times during mid-day. In certain embodiments, optical elementsare utilized in connection with a TDD in order to increase the amount ofsunlight captured by the TDD during morning and/or evening hours, ortime during which the Sun is at a relatively low solar altitude.

The tube 24 may comprise any number of segments or portions. Forexample, the embodiment depicted in FIG. 1 shows a tube 24 comprising anupper segment 24 a, an intermediate segment 24 b, and a lower segment 24c. The upper segment 24 a may be engaged with the flashing 22 andcovered by the light collector 20. The intermediate segment 24 b may becontiguous to the upper segment 24 a, and may be angled relativethereto. In certain embodiments, the tube 24 comprises multipleintermediate segments. For example, the tube 24 may comprise an upperintermediate segment that is configured to be slidably engaged with alower intermediate tube segment, thereby allowing for absorption ofthermal stresses in the tube 24. The lower segment 24 c may becontiguous to the intermediate segment 24 c, and may be connected to thetube 24. The one or more segments of the tube 24 may be configured suchthat the tube 24 provides a desirable pathway between the lightcollector 20 and the diffuser 26. In certain embodiments, connections,or joints, between contiguous tube segments are covered or sealed withtape or some other means in order to prevent leakage of sunlightpropagating through the tube 24.

In order to direct a greater portion of light that strikes the lightcollector 20 into the tube, optical elements may be incorporated intothe light collector to bend or direct sunlight in a direction generallytoward the tube aperture. In certain embodiments, the bending of lightis accomplished using prisms. The bending of sunlight using prisms canbe described by Snell's law of refraction, which sets forth therelationship between the angle of incidence of the daylight on thesurface of the light collector 20, and the angle of refraction of thelight after passing through the interface between the surface of thelight collector 20 and the air, or other substance, surrounding thelight collector. The degree to which the collector 20 bends light maydepend on a number of factors. For example, the index of refraction ofthe material or materials with which the collector 20 is constructedaffects the angle of refraction. In general, the greater the differencebetween the index of refraction of the cover and that of the surroundingair, the larger the angle of refraction. Furthermore, the incident angleof the light with respect to the index change interface affects theresulting angle of refraction. In general, the greater the incidentangle to the interface, the larger the angle of refraction. Lightentering a higher index material will refract toward the normal of thesurface of the interface. Conversely, light entering a lower indexmaterial will refract away from the normal of the surface of theinterface.

The amount of light transmitted through the light collector 20 may beaffected by first surface reflection losses, in the case of lightentering a larger index material, and total internal reflection losses,in the case of light entering a lower index material.

The various parameters described above influence the amount anddirection of light that passes through the collector 20 and into thetube 24. In certain embodiments, light collector 20 is configured tooptimize the amount of light collected, as well as the direction oflight propagation into the tube 24.

In certain embodiments, the tubular daylighting device 10 includes athermal insulation subsystem (not shown), or portion, that substantiallyinhibits thermal communication between the interior 12 of a building andthe outside environment 13. The thermal insulation subsystem can haveany suitable configuration, such as, for example, any configuration orcombination of configurations discloses in U.S. Patent ApplicationPublication No. 2011/0289869, the entire contents of which areincorporated by reference herein and made a part of this specification.

The tubular daylighting device may also include a thermal break in anymaterials or components of the daylight device that have high thermalconductivity. For example, a spacer or gap in the sidewall of the tube24 can be positioned near a thermal insulating portion and the thermalinsulating portion and thermal break can be configured to form asubstantially continuous layer between the building interior 12 and theexterior environment 13. In certain embodiments, the insulating portionand thermal break are disposed in the same plane as other buildinginsulation material, such as fiberglass or the like.

Tables A-D below provide data relating to the performance of fourdifferent daylighting device configurations, using two different lightcollection covers. The first cover, referred to herein as a reflectordome, is a substantially clear dome comprising a reflector affixedthereto on a portion of its inside surface. Such a dome is similar tolight collection cover embodiments described in US RE36,496 and/or U.S.Pat. No. 7,322,156, the entire contents of which are incorporated byreference herein and made a part of this specification. The second coveris a prismatic cylinder dome, which is described in greater detailbelow. The parameters measured include performance, solar heat gain(“SHGC”), and interior heat loss (“U-Factor”). The various daylightingdevice configurations represented in Tables A-D include open ceilingdesigns with insulation at the roof level, as well as light diffusers,such as the Optiview™ diffuser, manufactured by Solatube International,Inc. of Vista, Calif., USA. Performance of the various configurationscan be measured with respect to sunlight at varying solar altitudes.Specifically, the performance of each TDD configuration can be measuredwith respect to solar altitudes of 30° and 40°.

Table A provides performance data for a daylighting device configurationcomprising a straight tube with a single diffuser at its base and nothermal break or gap. As is demonstrated by the data, such aconfiguration may provide increased light spread and reducedefficiencies at relatively low solar altitudes. The performance data inTable A, as well as performance data in subsequent tables discussedbelow, are presented in terms of relative units of luminous flux withrespect to an arbitrary base value, rather than in terms of the SIderived unit, lumens. This is done in order to highlight the relativeperformance of the various embodiments described herein. Luminous fluxperformance data can be obtained with the use of a goniophotometer.

TABLE A Prismatic Cylinder Parameters Reflector Dome Dome Performance @30° 1.0 units luminous flux 1.43 units @ 40° 1.35 units 1.54 units SHGC.37/250 Btu/hr .26/175 Btu/hr U-Factor 1.27/245 Btu/hr Same (Btu/hr-sf-°F.)

Table B provides performance data for a TDD configuration comprising acollimator with a single diffuser at the base of the tube with a singlediffuser at its base and no thermal break or gap. As is demonstrated bythe data, such a configuration may provide reduced light spread andhigher efficiencies at relatively low solar altitudes.

TABLE B Prismatic Cylinder Parameters Reflector Dome Dome Performance @30° 1.0 units luminous flux 1.42 units @ 40° 1.35 units 1.36 units SHGC.37/250 Btu/hr .26/175 Btu/hr U-Factor 1.27/245 Btu/hr Same (Btu/hr-sf-°F.)

Table C provides performance data for a TDD configuration comprising acollimator with a diffuser thermal break at the level of roofinsulation. Such a thermal break can include clear and/or beadedglazings, which are supported and separated by a rigid insulatingmaterial (e.g., plastic component) with a seal.

TABLE C Prismatic Cylinder Parameters Reflector Dome Dome Performance @30° 1.0 units luminous flux 1.43 units @ 40° 1.40 units 1.59 units SHGC.31/210 Btu/hr .21/140 Btu/hr U-Factor .35/67 Btu/hr Same (Btu/hr-sf-°F.)

Table D provides performance data for a TDD configuration comprising acollimator with a diffuser “honeycomb” thermal break at the level ofroof insulation. Such a thermal break comprises clear and beadedglazings with honeycomb, which are supported and separated by a plasticcomponent with a seal.

TABLE D Prismatic Cylinder Parameters Reflector Dome Dome Performance @30° 1.0 units luminous flux 1.43 units @ 40° 1.39 units 1.59 units SHGC.30/200 Btu/hr .20/130 Btu/hr U-Factor .16/30 Btu/hr Same (Btu/hr-sf-°F.)

The tables above show that the prismatic cylinder dome may provide anincrease in performance and reduction in solar heat gain over reflectordome embodiments. Furthermore, configurations including a thermal breakmay significantly reduce solar heat gain and interior heat loss whencompared to certain alternative configurations. The configurationsconsidered above with respect to Tables A-D may be combined with, orincorporate, certain other features, components, or embodiments ofdaylighting systems as described herein, which may affect theperformance values measured above.

FIG. 2 illustrates an embodiment of the light collector 20 shown inFIG. 1. In certain embodiments, the light collector 20 is configured toturn at least a portion of the light striking its surface such that thelight is directed downwardly toward a horizontal aperture of the tube24. Various features and characteristics of the light collector 20affect the light turning properties of the collector. As disclosed inU.S. Pat. No. 7,546,709, the entire contents of which are incorporatedby reference herein and made a part of this specification, a lightcollector comprising a smooth outside curved surface in combination withinternal prisms may produce desirable light-turning effects. In certainembodiments, such a configuration provides a double refraction of thesunlight incident on the outside surface of the cover.

The light collector 20 may form any suitable shape and/or size. Forexample, light collector 20 may be generally cylindrically-shaped, witha flat or curved top portion. In certain embodiments, such as that shownin FIG. 2, the light collector 20 may be generallyhemispherically-shaped. The collector of FIG. 2 defines a closed apex240 and an open, generally circular base 242 opposite the apex 240.While the base 242 shown in FIG. 2 is circular, in certain embodiments,it may be elliptical, rectangular, or multi-sided, or any other suitableshape, or combination of shapes. The collector 20 may be configured tohave a continuous curved shape or a series of curved and/or flat sidessegments.

FIG. 2 depicts a prismatic pattern formed on the collector 20. Such apattern may be, for example, molded into the inside and/or outsidesurface of the collector 20. In certain embodiments, a prismatic film,or other prismatic element, is adhered to, connected to, or otherwiseassociated with the collector 20. As set forth in greater detail below,in certain embodiments, the prisms can be established by circulargrooves 244 that are parallel to the base 242 and that are defined byopposed faces that may have a flat or curved cross-sectional shape.Furthermore, as disclosed further below, the grooves 244 can vary indepth and pitch and/or in other respects. The grooves 244 maycircumscribe the entire circumference of the collector 20, and may besubstantially uniform throughout the height of the cover and around itsentire circumference. In certain embodiments, the grooves 244 vary withrespect to one or more parameters at different heights or points alongthe circumference of the collector 20. For example, the groves 244 maycomprise faces of varying angles, shapes, and/or widths, depending onheight and/or position. In certain embodiments, portions of thecollector 20 do not include a prismatic element. While the grooves 244are shown oriented as generally horizontal lines, a portion, all, orsubstantially all of the grooves 244 may be oriented at any suitablenonzero angle with respect to horizontal, or otherwise.

As shown in FIG. 3, the diameter of the collector 20 at the base 224 maybe greater than the diameter of the tube 24 at a horizontal aperture.For example, the diameter of the collector 20 at the base 224 may rangefrom 100% to 150% or more of the tube outer diameter. Furthermore, thecollector height, h, may range from 26% or less of the tube diameter to100% or more of the tube diameter.

The collector 20 may be formed with a variable prism that directslow-angle light into the skylight tube 24 and that reflects away atleast a portion of higher-angle light. Such a configuration may achievea more constant light output over the course of the day. In certainembodiments, grooves nearer the apex 240 of the cover have differentcharacteristics than grooves 244 nearer to the base 242. For example,FIGS. 4 and 5 provide cross-sectional views of embodiments of prismaticgrooves located in portions of the collector 20 near the apex 240 andthe base 240, respectively.

Grooves 244 may be defined by opposing faces (46, 48 with respect toFIG. 4, and opposing faces 50, 52 with respect to FIG. 5.) As shown inFIGS. 4-5, the angle of the pitch of the collector 20 (i.e., the anglebetween a line tangent to the curve of the collector and a horizontalplane) at each of the respective regions is labeled “α.” In certainembodiments, the pitch of the collector 20 is less at a point near theapex 240 of the collector than it is at a point closer to the base 242of the collector. Therefore, when the material out of which thecollector 20 is constructed has a constant index of refractionthroughout, light striking the cover may be turned to a greater degreetowards the tube in the region detailed in FIG. 4 than the regiondetailed in FIG. 5.

Light L_(S) strikes the surface of the cover 20 at a solar altitudeangle θ (e.g., 20° as shown in FIGS. 4-5). Therefore, the angle ofincidence at which the light strikes the collector 20 is equal to90°−(θ+α). In a case where θ=20° and α=22.5°, as shown in FIG. 4, theangle of incidence would be 47.5°. In certain embodiments, the materialof the cover 20 at the interface between the cover and the surroundingair has a greater index of refraction than the air. Therefore, at leasta portion of the light is refracted towards the normal of the surface bysome amount, depending on the angle of incidence as well as thedifference in indexes of refraction at the interface. In FIGS. 4-5, theangle of the refracted light after passing through outside air/coverinterface with respect to a horizontal plane (i.e., non-prismrefraction) is represented by “β.” The light further propagates throughthe wall of the collector 20 until it strikes a prism wall. In certainembodiments where the index of refraction of the cover is greater thanthat of the air or other material contained within the collector, lightpassing through the collector 20 will be refracted away from the normalof the prism surface. Prisms on the inside surface of the collector 20may be designed to further turn light towards a horizontal aperture ofthe tube 24. The angle between the prism face 48, 50 and a vertical axisof the tube is represented by “γ.” The additional angle of refractionexperienced by light L_(S) as it crosses the prism interface 48, 50 isrepresented by “δ.” Sunlight L_(S) entering the collector 20 maytherefore experience double refraction as it passes through twointerfaces of the cover, thereby potentially allowing for increasedlight-turning capability of the cover. As shown in FIG. 4, sunlightL_(S) strikes the surface of the collector at a solar altitude of 20°,at which point it is refracted downward by, for example, 18°. The lightL_(S) then strikes prism face 48, at which point it is again refracteddownward by, for example, an additional 7°. Therefore, after undergoingdouble refraction, light that enters the collector at a 20° angle withrespect to a horizontal plane, may be directed towards the tube at, forexample, 45° from horizontal, or some other angle, depending on theconfiguration of the collector (e.g., the configuration of any prismsused in the light turning assembly).

As depicted in FIG. 5, a may be greater at point nearer to the base 242than at a higher point. It may be desirable for cover 20 to beconfigured such that light entering the collector at a point nearer tothe apex 240 (e.g., point “A”) is turned to a greater degree than lightentering the collector at a point farther from the apex (e.g., point“B”) in order to direct such light into a vertically oriented tube 24.Table E below provides the total direction change of light passingthrough the top cover 20 for certain embodiments, as described below andillustrated in FIGS. 4-5. (Note: angles are referenced from horizontalunless otherwise noted).

TABLE E Light angle Prism “β” after angle Exterior non-prism “γ” (fromAdd'l surface refraction vertical) refraction Total angle through oflower “δ” direction “α” of cover outer prism through change of Covercover surface face prism face light Section (degrees) (degrees)(degrees) (degrees) (degrees) A (FIG. 5) 61 23 (3° 10 4 7 refraction) B(FIG. 4) 22.5 38 (18° 20 7 25 refraction)

In certain embodiments of dome-shaped covers such as that depicted inFIGS. 2-3, all or substantially all the low angle sunlight (e.g., lightwith a solar altitude angle of approximately 20°) entering the upperportion of the cover, i.e., at point “A,” enters the tube, therebyincreasing the effective aperture of the tube. Absent the prismaticelement illustrated in FIGS. 2-3, at least a portion of light that wouldotherwise be reflected downward into the tube 24 may exit the cover 20without entering the tube.

The dome-shaped light collector illustrated in FIGS. 2-3 may havereduced vertical sunlight capture area when compared with certainalternative light-collecting assembly configurations. For example, U.S.Patent Application Publication No 2010/0325979, the entire contents ofwhich are incorporated by reference herein and made a part of thisspecification, discloses a light collector with top cover and verticalsidewall portions. A light collecting assembly incorporating top andvertical collector portions can increase vertical sunlight capture areaby providing a large vertical target area for sunlight capture. FIG. 6shows a cross-sectional view of a light-collecting assembly comprisingboth a vertical portion 636, which spans a lower region 651 and a topcover portion 638, occupying an upper region 640. In certainembodiments, a prismatic film is disposed inside and/or outside of thevertical portion 636 to provide double refraction of light. For example,as illustrated in FIG. 6, the prismatic film 648 may include prisms 656facing outward to provide a first refraction of light and a planesurface of the sheet providing a second refraction. In certainembodiments, this prismatic pattern is molded into a thin polymer sheetthat can be placed inside of a protective transparent cover. In certainembodiments, prisms are formed in the outside or inside surface ofcollector 636. A top cover portion 638, such as, for example, theprismatic cover shown in FIG. 2, can be disposed above the verticalportion 636.

In certain embodiments, the collector assembly 620 is symmetrical,providing a 360-degree sunlight capture zone. The effective lightcapture area of the collector assembly 620 can be an area of thecollector directly exposed to rays of sunlight, plus the portion of thesurface area of the top cover that is directly exposed to the sunlight.In certain embodiments, in the presence of unobstructed, substantiallycollimated light, the effective capture area of the collector may beapproximately 90 degrees of the 360 degree perimeter of the collector,or approximately 25% of the total surface area of the collector. Incertain embodiments, a prismatic film 648 with outwardly-facing prisms656 runs along the inside of at least a portion 650 of the lower region651 of the collector 620. In certain embodiments, sunlight may refractdown into the tube if the sunlight is within approximately +/−45 degreesincident angle to the surface of the collector. Because the entiresunlight capture zone encompasses the full 360 degree perimeter, only 90degrees, or 25%, of the available area might be utilized in the presenceof clear, collimated sunlight.

In some embodiments, the top cover portion 638 is made integrally withthe vertical portion 636 and may extend from an open base 641 to aclosed apex 642 distanced from the open base 641, forming a continuouswall. The top cover portion 638 may be spherical, hemispherical, planar,curved, or may have some other closed form, such as a pyramid, cone, orany other suitable shape. The vertical portion 636 may be hollow, andmay extend from the open base 641 of the dome 638 down, terminating inan open lower end 646, through which light can pass.

As depicted in FIG. 6, the light collector 620 can include one or moreprismatic films 648, which can circumscribe an axial segment 650 of thevertical portion 651. Prismatic film 648 may be a single unitary member,or may comprise multiple distinct segments. In certain embodiments thatinclude a prismatic film 648, the prismatic film 648 may span the entirevertical portion 651 of the light collector 620. Alternatively, as shownin FIG. 6 the prism ring 648 may span a first axial segment 650 of thevertical portion 651, but not span a second axial segment 652 that iscontiguous to the first axial segment 50.

The top cover portion 638 may be formed with prismatic elements,generally designated 654, which may be prism lines that are etched in,molded in, or otherwise integrated with or attached to the top coverportion 638. In certain embodiments, the prism elements increase lightthroughput by capturing light originating outside the collector 620 andturning it downward through the open periphery 641, past the verticalportion 651, and into a tube assembly. The prism lines 654 may beoriented parallel to a horizontal plane, and may entirely circumscribethe top cover portion 638 in concentric circles. Example embodiments ofprism lines 654 are described in more detail below.

In certain embodiments, sheet 648 may include prisms, generallydesignated 656, configured to refract light. Prisms 656 may compriseprism grooves on an outer surface 658 of the prismatic film 648, and maybe linear when the sheet is in a flat configuration and, thus, formcurved sections when the sheet 648 is shaped into the configurationillustrated in FIG. 6. The outer surface 658 of the prismatic film 648may be positioned against, or proximate to, an inner surface 660 of theaxial segment 650 of the vertical portion 636. The prism grooves 656 maybe outwardly facing, as shown in FIG. 6, or otherwise configured. Incertain embodiments, prisms 656 are similar to the prism elements inembodiments of the top cover portion 638 in that they capture light fromoutside the collector 620 and turn it downward into a tube assembly,thereby increasing light throughput.

In certain embodiments, the prisms 654 associated with the top coverportion 638 are similar to embodiments of prisms associated with thedome described above with respect to FIG. 2. For example, the prismelements 654 may have varying prism angles depending on what portion ofthe dome they are associated with. In certain embodiments, the prismelements 654 have uniform prism angles throughout the top cover portion638.

In certain embodiments, prisms within the same portion of the top cover640 or vertical portion 651 have varying prism angles. FIG. 7illustrates a cross-sectional view of a segment of a transparent domehaving a plurality of prisms 756. In certain embodiments, the prismangles of prisms 756 may vary relative to one another. For example, γ₁(e.g., 20°) which represents the prism angle of prism 756 b, isdifferent than γ₂ (e.g., 9°), which represents the prism angle of prism756 a. It may be desirable for adjacent prisms, or adjacent groups ofprisms, to comprise different prism angles in order to mix the lightthat propagates through a light collector. For example, if substantiallycollimated light enters a prismatic portion of a light collectingassembly that comprises prisms with equal prism angles, light enteringthe tube may be concentrated in certain regions. Such lightconcentration may cause undesirable “hot spots” in the destination area.By varying the prism angles, the effect of such hot spots may bereduced.

FIG. 8 provides a cross-sectional view of a portion 848 of the prismaticfilm 648 shown in FIG. 6. The portion 848 of the prismatic film 648shown in FIG. 8 comprises a plurality of prisms 856. The assembly shownin FIG. 8 comprises an outer transparent vertical portion 636 of thelight-collecting assembly 620 of FIG. 6. The prisms 856 may bepositioned along the interior surface 660 of the transparent verticalportion 636, and may face the direction of sunlight L_(S) penetratingthe vertical portion 636. In certain embodiments, prisms 856 areinwardly facing, with back surface 849 lining, or proximate to, outervertical portion 636. In certain embodiments, prismatic film 848contains prisms on more than one of its sides. The prisms may beconfigured to turn at least a portion of sunlight that strikes thevertical portion of the light collecting assembly downward towards ahorizontal aperture of a tube.

In certain embodiments, prisms 856 include two faces 846, 848. In theembodiment of FIG. 8, face 848 has a prism angle γ₁ with respect tohorizontal (e.g., 50°), while face 846 has a prism angle γ₂ belowhorizontal (e.g., 30°). Prism angles γ₁ and γ₂ may be equal, or mayvary, depending on the configuration of prismatic film 850. Furthermore,similarly to prisms 756 described above, adjacent prisms 856, or groupsof prisms, may have varying prism angles. Such varying prism angles maypromote mixing of light propagating through a light collector. Incertain embodiments prismatic film 850 comprises prisms having uniformprism angles.

With further reference to FIG. 6, prism angles of the dome 638 and theprismatic film 648 may be designed to provide an incident angle to theSun that increases or maximizes the range of solar altitude radiationthat may be captured and turned toward the aperture 646 at the base ofthe light-collecting assembly 620. In certain embodiments, the dome 638and prismatic film 648 are comprised of the same material or materials,or materials having substantially similar indexes of refraction. Incertain embodiments, the prismatic film 648 can comprise a material ormaterials with higher index of refraction than the dome 638.

The vertical portion 636 may be configured to capture relatively lowangle sunlight, such as, for example, sunlight at a solar altitude ofaround 20°. In certain embodiments, the vertical portion 651 has anaspect ratio (vertical height to horizontal aperture) of greater thanapproximately 0.91. Increased height of the vertical portion 651 mayadvantageously increase the effective capture area of the horizontalaperture 646 during times of relatively low solar altitude, therebyproviding increased sunlight during the morning and late afternoon/earlyevening hours. In addition to increasing the effective aperture of askylight at low solar elevations, the vertical portion 636 may also beconfigured to reduce the effective capture area of the horizontalaperture 646 at higher sun angles to prevent over illumination and/orheating during midday hours.

Table F, below, provides refracted angles of light that is refractedusing a light turning assembly with two different prism angles. Each ofthe rows of the table is associated with sunlight at a different solaraltitude, as identified in the first column. The second and thirdcolumns provide the refracted angle of light (measured from horizontal)after the light passes through the respective portion of the prismaticelement. In some embodiments, light enters a light collector assemblythat includes two or more prism angles (e.g., 50° and 70°). Daylightwill not pass through the prismatic element when the incident angle oflight on the prismatic surface (e.g., as determined by the solaraltitude, the orientation of the prismatic element, the angle of anyreflector that directs light towards the prismatic element, and/or andthe prism angle of the prismatic element) exceeds the critical angle oftotal internal reflection (“TIR”). When TIR occurs, substantially noneof the light incident on that portion of the prismatic element entersthe light collection assembly. When a reflector is used to directdaylight towards the prismatic element, the angle(s) of the prismaticelement can be selected to increase or maximize the amount of direct andindirect (e.g., reflected) daylight that is directed into a tubeaperture.

TABLE F Solar Altitude Angle of Refracted Light Angle of Refracted Light(degrees) (Prism Angle of 50°) (Prism Angle of 70°) 20 42° 31° 30 55°42° 40 74° 55° 50 TIR 72° 60 TIR TIR

The top of a light collecting assembly can be clear or prismatic. Aprismatic top cover portion can have a prismatic element having a singleprism angle or multiple prism angles. A clear top cover application maybe beneficial in highly diffuse climates due to relatively hightransmission of overhead sunlight. In certain embodiments, at least aportion of the top cover portion 638 may be configured to reflect someor all of the light striking such portion at solar altitudes above acertain angle. For example, a portion of the dome at or near the apex642 may be configured to reflect at least a portion of overhead sunlightin order to reduce light and/or heat during midday hours.

The vertical portion 636 may comprise any suitable shape or combinationof shapes. For example, the portion 636 of light-collecting assembly 620may have a square, circular, elliptical, triangular, hexagonal, orotherwise shaped base. Furthermore, the walls of the portion 636 may besubstantially vertical, or may have any desired inward or outward slope.In certain embodiments, the walls of vertical portion 636 are sloped toallow for nesting of multiple such components for tighter packaging.

In certain embodiments, the vertical portion 636 provides asubstantially vertical target area for sunlight collection, which mayprovide higher aspect ratios for light collection. Prismatic elementsmay be integrated with at least a portion of the wall of the verticalportion 636. In alternative to, or in addition to, prisms integrated inthe vertical portion 636, the above-described prismatic film may be usedto refract light downward. The planar back side 849 of the prismaticfilm, shown in FIG. 8, may provide good downward refraction due to ahigh to low index of refraction interface. In certain embodimentscomprising a plastic polymer with an index of refraction in the range ofapproximately 1.49-1.65, the vertical portion of the collector can havean aspect ratio of height to width that is greater than or equal to 0.9.In some embodiments, the vertical portion's aspect ratio of height towidth is greater than or equal to 1 or greater than or equal to 1.1.

Table G, below, provides computer simulation data comparing theperformance of a conventional 21-inch diameter clear dome lightcollecting assembly to that of an embodiment of a cylinder-dome lightcollecting assembly having a height of 23 inches, constructed accordingto principles disclosed herein. The table provides the amount of light(in relative units of luminous flux) collected by each of the respectiveassemblies at various solar altitudes. These performance values includethe associated direct solar illuminance at each solar altitude. Thesevalues can be obtained using the procedures set forth by theIlluminating Engineering Society of North America (IESNA), which aredocumented in Section 5.5 of the IESNA 9^(th) Edition Handbook, chapter8.

TABLE G Solar Altitude (degrees) Clear Dome Cylinder-Dome 20  1.0 unitsluminous flux 2.02 units 30 1.43 units 2.31 units 40 2.02 units 2.50units 50 2.29 units 1.86 units 60 2.67 units 1.53 units 70 2.92 units1.06 units

Table G demonstrates an increase in light collection at solar altitudesof 40 degrees or less. Therefore, in certain embodiments, cylinder-domelight-collecting assemblies provide increased light collection duringperiods when conventional light-collecting assemblies fail to capturesubstantial amounts of light, such as during certain morning and/orevening hours, depending on the time of year and/or latitudinalposition. Furthermore, light collection may be reduced during periodswhen the amount of light sunlight exposure is more than may bedesirable, such as during midday periods. In certain embodiments, lightcollecting assemblies in accordance with embodiments disclosed hereinprovide for fewer reflections of light as it propagates down a tubebecause light is turned to more closely align with a longitudinal axisof the tube. Fewer reflections within the tube may decrease losseswithin the tube. Moreover, light propagating through the tube may reacha diffuser at the base of the tube at smaller incident angles, providingfor higher optical transmission efficiencies. In addition, as isdemonstrated by Table G, a cylinder-dome configuration may allow for amore uniform supply of illumination throughout the day.

As discussed above, the top cover portion of a light collector assemblymay be substantially hemispherically shaped, as illustrated in FIG. 2,or may be any other suitable shape. The example light collectingassembly in FIG. 9 comprises a conically shaped top cover portion 938.Similarly to some of the embodiments described above, the top coverportion 938 may be integrated with one or more light-turning assemblies,such as prisms, for bending sunlight downward. A top region of the dome938, such as circular region 942, may be configured to reflect some,all, or substantially all of sunlight at high solar altitudes, therebydecreasing the intensity of light during midday hours. FIG. 10 providesa top view of the conical top cover portion 938 of FIG. 9

FIG. 11 illustrates an embodiment of a light-collecting assemblycomprising a top cover portion 1138 including multiple collectorsegments 1138 a, 1138 b, 1142. The walls of one or more of the wallsegments may be substantially straight, or may be curved to some degree.At least a portion of each of the wall segments 1138 a, 1138 b caninclude a light turning element. With respect to the embodimentillustrated in FIG. 11, the walls of collector segments 1138 a and 1138b have different surface angles with respect to a horizontal plane.Collector segment 1138 b may be configured to bend low angle light to agreater degree than collector segment 1138 a. This may be desirablebecause light striking the top cover portion 1138 at segment 1138 b mayrequire a greater change in direction in order to enter the horizontalaperture of the tube below.

Depending on the Sun's altitude and/or azimuth, the effective lightcapture area of a roof-top collector with respect to direct sunlight maynot incorporate a majority of, or at least a portion of, the availablesurface area of the light collector. For example, with respect to atleast low-altitude sunlight, at least a portion of the surface area of alight collector that is opposite the Sun's rays may not capture anydirect sunlight. It may therefore be advantageous to expose a greaterportion of the total surface area of a light collector to sunlight,whether direct or indirect, in order to increase the light-capturingcharacteristics of the light collector. One way to accomplish this maybe to position a visible light reflective element in such a way as toreflect a portion of sunlight towards the capture area of the lightcollector. Such a reflective element may be passive or may be configuredto track the location of the Sun throughout the day.

In certain embodiments, a flat or curved reflective panel is positionedgenerally behind a light collector. The reflector reflects sunlight ontoa vertical target area of a light collector. The vertical target areacan be larger than the horizontal aperture of a tube in a skylightapplication. A light turning system connected to the light collector canturn the light downward towards a collector base aperture and into thetube. The light turning system can include a prismatic element, arefractive element, a reflective element, other optical elements, or acombination of optical elements. FIG. 12 provides a perspective view ofan embodiment of a sunlight-collection system comprising a lightreflector 1280 positioned in proximity to a light collector 1220. Thereflector 1280 may be positioned any distance from the light collector1220, and the distance between the reflector 1280 and the lightcollector 1220 may vary at different points of the reflector 1280.

The light collector 1220, similarly to certain embodiments disclosedabove, may comprise a vertical portion 1236 and a top cover portion1238. In certain embodiments, light reflector 1280 is parabolicallycurved about light collector 1220. As is shown in FIG. 13, whichprovides a top view of the sunlight collection system of FIG. 12, theparabolic light reflector may be positioned such that the center oflight collector 1220 lies on the axis of symmetry of the parabola 1280at the focus point. Such a configuration may provide increased captureof reflected sunlight by the vertical capture area of the lightcollector 1220 when the reflector 1280 is positioned such thatsubstantially collimated direct sunlight that strikes the reflector 1280is substantially parallel, or within an acceptable range of anglesrelative to parallel, to the axis of symmetry of the parabola 1280.Light striking the parabolic reflector 1280 at any point along itslength, or at least over a portion of its length, may be reflectedtowards the vertical capture area of the light collector 1220.

Reflectors 1280 suitable for use with embodiments of daylighting systemsdisclosed herein may include the Vega WR 193 and 293 model outdoorenvironment reflectors, manufactured by Almeco USA Inc. of Atlanta, Ga.,USA, and/or the MIRO-SUN weatherproof reflective 90 and weatherproof 85model reflectors, manufactured by Alanod Westlake Metal Ind. of NorthRidgeville, Ohio, USA. Such products may be formed into various shapes,such as parabolas, and may provide excellent solar reflective propertiesand withstand harsh outdoor environments. In some embodiments, thereflector has a luminous reflectance greater than or equal to about 95%,greater than or equal to about 98%, or greater than or equal to about99% when measured with respect to CIE Illuminant D₆₅.

The light reflector 1280 of FIG. 12 is curved about the light collector1220. However, as discussed below with respect to the exampleembodiments of FIGS. 16-18, light reflector 1280 can have any desirableshape or configuration. The reflector 1280 may collect substantially ornearly collimated/parallel sunlight rays and redirect them to a commonfocal line. The reflector 1280 may be positioned behind the collectorwith its focal point at or near the center of the collector 1220. Such aconfiguration may allow for sunlight to be directed to the verticalportion and top cover faces in line with a vertical plane that rotatesaround the center of the collector 1220. This may increase the sunlightcollection area and utilize a greater portion of the total area and/oroptics of various lenses in the collector 1220.

The use of a curved reflector 1280 may allow for sunlight capture from agreater range of circumferential angles about the light collector 1220.This increase in angular capture of sunlight may provide a number ofbenefits, such as increased light mixing. For example, in embodiments inwhich sunlight enter a tube opening from a wide range of circumferentialangles, the distribution of light exiting the tube may be more uniformand may reduce the presence of hot spots on a diffuser at the base ofthe tube. Such light mixing may also prevent collimated light fromreaching the diffuser prisms in such a way as to cause rainbows toappear in the building interior.

With respect to certain embodiments in which light is directed into acentral feeder tube, and dispersed into multiple branch tubes, lightmixing may be important in promoting the dispersion of sunlight into thevarious branch tubes. In certain embodiments, branch tubes each receiveapproximately equal amounts of light from the central feeder tube.

The collection and redirection of sunlight using a light reflector, suchas the curved reflector 1280, may substantially increase the performanceof a conventional tubular daylighting device. A number of parameters maycontribute to increased performance of certain embodiments ofsunlight-collection systems. For example, the sunlight collection areaof the vertical portion 1236 of light collector 1220 may affect theperformance of such a system. In certain embodiments, the height anddiameter of the vertical portion 1236 in relation to the diameter of atube opening into which light is directed may be determined by therefractive turning power of optical elements (e.g., integrated prisms,prismatic film or lensfilm, etc.) within, or associated with, thecylinder. This aspect ratio of cylinder height to tube diameter maydepend on the solar altitude range it is desired to capture and refractinto the tube. This range may be from approximately 20 to 70 degrees formost locations in the United States. For example, using lower-end solaraltitude of approximately 20 degrees as the design point for refractinglight into the tube from the optical elements associated with avertical-walled cylinder, the cylinder height may be designed to anapproximate range of 0.67 to 1.0 times the tube diameter. These valuesmay vary based on material index of refraction and prism angles, amongother things.

In some embodiments, a vertical portion 1236 of a light collector has anaspect ratio of cylinder height to tube diameter of approximately 0.67.The effective sunlight collection area of a collector having thisconfiguration can be calculated. The sunlight-capture surface areas ofthe cylinder with respect to both direct and reflected light aremeasured in a vertical plane. The parabolic reflector may be positionedsubstantially vertically parallel to the outside wall of the verticalportion 1236, such that reflected light enters the vertical portion 1236at an angle of incidence approximately equal to the solar altitude.

As an example, a system may include a collector height of approximately9.125″ and a tube diameter of approximately 13.6″. The width of thevertical portion 1236 may be approximately equal to the diameter of thetube opening, or may be larger or smaller than the diameter of the tube.For example, the vertical portion 1236 may have a diameter ofapproximately 15.6″. The actual effective front light-capture area ofthe cylinder is associated with the direct non-reflected sun, which, incertain embodiments, may be limited to an exposure angle ofapproximately 90 degrees (a chord width of approximately 11″) due to theoff axis curvature limitation of the optics in the vertical portion andtop cover portion lenses. The effective direct sunlight capture area ofthe collector is therefore:

11″×9.125″=100.4 in².

As shown in FIG. 13, in certain embodiments, the reflected sunlight fromthe parabolic reflector may be designed for a 212 degree (+/−106 degreefrom the back side of the cylinder) coverage of the collector perimeter,which, according to the specifications described above, has thefollowing reflected sunlight capture area:

15.6″×3.14×9.125″×)(212°/360°)=263.2 in².

Referring to FIG. 14, the effective sunlight collection area of the topcover portion 1438 depends on, among possibly other things, the height1406 of the top cover. The height 1406 of the top cover may be based onthe refractive optics required to redirect the sunlight down the height1401 of the collector to the tube opening. In certain embodimentsincorporating a double-refractive optical element from the exterior ofthe dome and the internal prisms, the height may be determined by theslope a of the dome, prism angles, and/or material index or indices ofrefraction. In an embodiment comprising a slope a of about 35 degreesfrom horizontal and a prism riser angle of about 9 degrees from verticalwith an included angle of about 58 degrees, the dome may have a heightof approximately 5.4 inches. The total area of the dome would beapproximately equal to a right circular cone at 35 degrees fromhorizontal (3.14×7.8″×9.5″=232.7 in²), depending on how closely the domeconformed to the shape of a cone. In certain embodiments, the shape ofthe dome varies in certain respects from an exact cone. For example, theapex 1442 of the dome may be rounded off, rather than pointed, amongother possible variations. In a system in which the surface of the domefacing the sun has an acceptance angle of approximately 90 degrees, thedirect sunlight capture area may equal approximately 44.9 in². Thereflected sunlight portion (acceptance angle of 212 degrees) would beapproximately 137.0 in².

Table H summarizes calculated individual and total sunlight collectioneffective areas in relation to solar altitude. The table includes theeffective sunlight collection areas of the cylinder-dome designdescribed above at solar altitudes of 20 to 70 degrees in 10 degreeincrements. The values in the table take into consideration the cosinedifference between the suns solar altitude from horizontal and theincident angle to the plane of the vertical cylinder and the slopeddome. The values in the table provide only potential area for lightcollection for demonstration, and may not take into account certainlosses that may be experienced in lighting systems actually constructedaccording to the principles disclosed herein, such as material opticaltransmission losses.

TABLE H Light Incident to Collector Vertical Surface Including LightIncident to Dome Direct + Reflected Surface Including Direct + TotalSolar Sunlight Reflected Sunlight Effective Altitude (% direct/total (%direct/total effective Area for (degrees) effective area) area)Collector 20 29/341.6 in² 24/147.1 in² 510.7 in² 30 27/316.3 in²24/163.3 in² 479.6 in² 40 28/278.0 in² 24/174.0 in² 452.0 in² 5028/232.7 in² 24/179.4 in² 412.1 in² 60 28/181.8 in² 24/179.4 in² 361.2in² 70 28/123.6 in² 24/174.0 in² 297.6 in²

Table I, below, provides calculations of the collection area of a cleartop cover, as opposed to the collector comprising secondary opticsdescribed above, using a parabolic reflector. The effective capture areaof a horizontal aperture of a tube opening may be calculated using thearea of a right circular cone. Similar to the embodiment describedabove, the horizontal aperture (i.e., the tube opening) may beapproximately 13.6″ in diameter and have an area of approximately 145int. The direct sun front area is a factor of the sine of the solaraltitude times the horizontal area. The reflected light may again spanapproximately 212 degrees of the full circumference of the tubeaperture. This application may represent the use of the parabolicreflector with only a clear top cover covering the tube opening. With aparabolic reflector vertically oriented, reflected light retainsapproximately the same solar altitude value as direct sunlight. Inembodiments comprising a reflector that is tilted either forward orbackward by some amount, reflected light may have a different solaraltitude than direct light.

Again, the following table summarizes the individual and total sunlightcollection effective area in relation to solar altitude. The values inthe table provide only potential area for light collection fordemonstration, and may not take into account certain losses that may beexperienced in lighting system actually constructed according to theprinciples disclosed herein, such as material optical transmissionlosses.

TABLE I Direct Sunlight Incident to the Front of the Reflected SunlightTotal Effective Horizontal Incident to Horizontal Area for a Clear SolarTube Opening Tube Opening Dome/Horizontal Altitude (% available/ (%available/effective Opening (degrees) effective area) area) w/Reflector20  34/49.4 in²  34/90.9 in² 140.3 in² 30  50/72.6 in²  50/98.7 in²171.3 in² 40  64/92.9 in² 64/111.7 in² 204.6 in² 50 77/111.8 in²77/133.0 in² 249.8 in² 60 87/126.3 in² 87/171.0 in² 297.3 in² 7094/136.5 in² 94/249.9 in² 386.4 in²

With further reference to FIG. 13, the effective sunlight collectionarea of the parabolic reflector 1280 may depend on a number ofparameters, such as shape, size, secondary optical elements, etc. In theembodiment depicted in FIG. 13, the shape of the a verticalcross-section of reflector 1280 is based on the standard form equationy²=4px for a parabola, where p is the focal distance from the vertex, v,and the x-y coordinates provide the shape. In certain embodiments, itmay be desirable to locate the vertex near to the outside perimeter ofthe collector, or as close as practical or possible. In certainembodiments, the center of the collector is positioned at or near focalpoint of the parabolic reflector 1280. For example, with a collectorwidth of about 15.6″, it may be desirable to position the center of thecollector at a focal distance of about 9″ and configure the reflector1280 to have an aperture 1281 across the curve of the reflector to thesun of about 48″. This configuration may provide the approximately 212degree coverage of the collector perimeter on which certain calculationsabove depend.

With reference to the embodiment daylighting system shown in FIG. 14,the collector 1220 may have any suitable height 1401, and such height1401 may depend on a number of parameters, such as tube aperturediameter, specifications of secondary optics incorporated in orassociated with the collector, amount of desired light collection, cost,manufacturing concerns, and/or other parameters. In certain embodiments,the height 1401 of the collector is approximately 14.6″, greater than orequal to about 10″, greater than or equal to about 14″, or anothersuitable height.

The reflector 1280 may have any suitable height 1403. For example, theheight 1403 of the reflector may be substantially equal to the height ofthe light collector, or may have a height greater than that of thecollector to accommodate a range of vertical tilts, as discussed ingreater detail below. For example, in an embodiment comprising a 14.6″tall collector, the reflector 1280 may have a height of 16″.Furthermore, the reflector may be raised by a certain amount 1402 withrespect to a roof top or the base of the light collector 1220.Therefore, the top of the reflector 1280 may be a total distance 1407above a roof top or the base of the light collector 1220.

FIG. 16 provides a cross-sectional view of a vertically-oriented planarreflector 1680. As is shown in the figure, the angle θ₁ of direct lightL_(D) with respect to a horizontal plane is generally equal to the angleto the angle θ₂ of reflected light L_(R). In certain embodiments, it maybe desirable to tilt a light reflector about an axis, thereby alteringthe angle of reflected light. FIG. 15 illustrates an embodiment of asunlight collection system in which a light reflector 1580 is configuredto tilt about a horizontal axis at pivot point p at the base ofreflector 1580. While pivot p is located at the base of reflector 1580,the reflector may be configured to tilt or rotate about any suitablepoint. For example, reflector 1580 may be configured to pivot about at apoint approximately midway between the top and base of the reflector.The reflector 1580 may be configured to tilt forward, backward, or bothforward and backward. As shown in FIG. 17, which provides across-sectional view of a planar reflector 1780 tilted 5° towards thedirection of direct light L_(D), tilting the reflective panel forwardwill generally change the resultant solar altitude 10 degrees for every5 degree panel tilt from vertical, and tilting back from vertical willdecrease the resultant solar altitude according to the same ratio.Specifically, in the embodiment of FIG. 17, the angle θ₂ of reflectedlight L_(R) with respect to a horizontal plane is 10° greater than theangle θ₁ of direct light L_(D).

Under certain lighting conditions, it may be desirable to tilt reflector1580 forward in order to direct light downward. For example, FIG. 15shows reflector 1580 a tilted forward by an amount θ₁. During times oflow solar altitude, such as morning or evening hours, it may bedesirable to tilt the reflector 1580 a forward in order to capture anincreased amount of sunlight in light collector 1520. In embodimentscomprising a clear light collector with a horizontal light capturetarget area, a greater degree of tilting may be desired than inembodiments comprising a light collector with a vertical light capturetarget area.

When sunlight is at a high solar altitude, such as during the middle ofthe day, it may be desirable to tilt the reflector 1580 b backwards inorder to reflect light towards the target light capture area of a lightcollector. For example, FIG. 15 shows reflector 1580 b tilted backwardby an amount θ₂.

The tilt angle of the reflector may be fixed at a certain point, such asa point calculated according to a median value for performance. Incertain embodiments, the sunlight collection system 1500 comprises amechanism for tilting the reflector 1580 throughout the day to track thesolar altitude of the Sun. Such a mechanism may be relatively tolerant.In certain embodiments, light reflector 1580 is configured to bothrotate about light collector 1520 to track the Sun's solar azimuthangle, as discussed above, and to tilt to track the Sun's solaraltitude. For example, light collection system 1500 may comprise a guidetrack on which light reflector 1580 rotates, wherein the guide trackeffects tilting of the reflector 1580 by an amount associated with therotational position of the reflector.

While many of the embodiments described herein are described in thecontext of light collection systems incorporating curved, or parabolic,light reflectors, light reflectors in accordance with the embodimentsdescribed herein may be any suitable shape, size or configuration, andmay comprise a single reflector, or multiple reflectors. For example, areflector for use in a sunlight collection system may be planar,circular, spherical, semi-spherical, elliptical, rectangular, or anyother shape or combination of shapes. Furthermore, a reflector may becurved or angled in any direction or dimension. In certain embodiments,a reflector is parabolic either the along a horizontal axis, a verticalaxis, or both. In addition the shape of a reflector may vary based onthe distance of a particular portion of the reflector to a target, suchas a light collector. FIGS. 18-20 provide non-limiting exampleembodiments of reflectors for use in a sunlight collection system.

FIG. 18 illustrates an embodiment of a reflector 1880 incorporated in alight collection system having a generally straight configuration. Sucha reflector 1880 may be passive or may rotate about light collector1820. Furthermore, reflector 1880 may be elevated, such as by beingdisposed on, or integrated with, stilts or other elevating assembly.Unlike a parabolic reflector, reflector 1680 does not curve about lightcollector 1620. Such a reflector may be cheaper and/or more efficient tomanufacture, ship, install, etc. However, a straight reflector may notprovide as much captured reflected light as a curved reflector.

Static/passive and active reflective systems described herein may bedesigned around the concept that capturing sunlight with a reflectivesurface and directing it to a vertical versus a horizontal target can bemore effective. One reason for this may be based on the reduction of theincident angle between the reflective panel surface and direct sunlight,thereby increasing the density of light on the panel. This concept isdemonstrated in Table K, below. Table J, below, provides performancedata obtained using a goniophotometer of static/passive and activereflector designs along with a prismatic collector and a segmentedcollimator at the base of the tube. The tests can be performed at fivesolar altitudes (20 to 60 degrees in 10 degree increments). The systemsrepresented in Table J use a 14″ diameter tube and roof opening, 1square foot aperture, and a collimator at the base of each design. Incertain embodiments, as supported in the table, a daylighting system inaccordance with configurations disclosed herein may provide enough lightfrom a single square-foot aperture in a roof to displace approximately 2175-watt metal halide high bay lamps. Data relating to the various lightcollection assemblies is provided to illustrate the performancedifference between the devices. These performance values include theassociated direct solar illuminance at each solar altitude.

TABLE J PCD With PCD With Prismatic Passive Active/ Clear Dome CylinderDome Reflector Parabolic System With (PCD) With and Reflector and DesignCollimator Collimator Collimator Collimator 20 Degrees 1.0 (units 1.692.21 7.98 luminous flux) 30 Degrees 1.72 2.43 2.88 10.98 40 Degrees 2.312.34 3.89 13.20 50 Degrees 2.86 1.98 4.77 12.68 60 Degrees 3.36 1.705.47 11.35

As demonstrated in Table J, a prismatic top cover design may increaseperformance with respect to a clear top cover at lower solar elevationsand reduce performance at higher angles to prevent glare and theassociated heat gain. Furthermore, a prismatic top cover design mayprovide better average performance for the day.

As shown, a passive design may increase performance at all solarelevations between at lease 20 and 60 degrees, especially with respectto higher elevations for configurations optimized to reflect light intothe prismatic collector. With respect to an active design, performancemay be increased substantially because light may be reflected into thecollector around greater than 212 degrees of the 360 degree perimeter ofthe top cover, in certain embodiments. Furthermore, certain embodimentsmay be configured to maintain/control the amount of light captured bytilting a parabolic reflector based on performance requirements and/orthe sun elevation.

The light reflector 1980 shown in FIG. 19 comprises a plurality ofreflective panels that bend around light collector 1920. Each of thepanels 1980 a, 1980 b, 1980 c is substantially straight, but each liesin a plane at a different axial angle with respect to the vertical axisof light collector 1920. The shape of reflector 1980 may approximatethat of a parabolic reflector, except with discrete straight segments asopposed to a continuous parabolic curve. The various panels of reflector1980 may be adjustably rotatable with respect to one another. Forexample, the angle θ between two panels may be manually or otherwiseadjustable as desired. The reflector 1980 may be passive or may rotateabout light collector 1920.

One or more portions or segments of a light reflector in accordance withembodiments disclosed herein may be raised with respect to otherportions or segments of the reflector. In the embodiment of FIG. 20, theperipheral end portions 2080 a, 2080 c of light reflector 2080 areraised by an amount h₂ with respect to the central portion 2080 b. Incertain embodiments, peripheral end portions of a reflector, such as theperipheral portions of a parabolic reflector, are positioned furtherfrom the center of an associated transparent cover than are more centralportions. This variation in distance between the reflector and thetransparent cover can lead to uneven collection and distribution oflight. For example, in certain embodiments, downwardly-angled lightreflected from farther distances must generally originate from avertically higher position in order to reach the transparent cover thanif the light were reflected from a closer position. Therefore, it may bedesirable to raise peripheral ends of a reflector in order to promoteeven collection and distribution of light. Variation in height inportions of a reflector may comprise one or more generally discretesteps, such as in the embodiment of FIG. 20, or may be gradual. Incertain embodiments, the top of the reflector is raised at certainportions, such as peripheral end portions, while the bottom edgemaintains a continuous vertical position. In such embodiments, theheight h of the reflector 2080 may vary over its width.

As described above, relative variation in height or size of portions ofa light reflector may reduce potentially undesirable effects ofvariation in distance between the reflector and the light collector. Incertain embodiments, optical elements integrated in or associated with areflector may help reduce such effects. For example, peripheral endportions of a light reflector, or any other portion of a reflector, maycomprise prisms for altering the angle and/or direction of lightreflecting off the reflector's surface. With respect to FIG. 20, ratherthan, or in addition to, raising peripheral end portions 2080 a and 2080c, such portions may comprise optical elements that bend light upward bysome amount in order to compensate for the greater distance lightreflected off such portions must travel. In certain embodiments, opticalelements associated with bottom portions of a reflector bend lightupward, and/or optical elements associated with one or more top portionsbend light downward. With respect to the rectangular reflector 1880 ofFIG. 18, reflector 1880 may comprise optical elements that bend lightincreasingly inward moving away from the center of the reflector.Furthermore, optical elements in an upper region of the reflector 1880may turn light to a greater degree than optical elements in a lowerregion. In certain embodiments, optical elements associated withreflector 1880 approximately simulate light reflection characteristicssimilar to that of a parabolically or otherwise curved or configuredreflector. By associating optical elements with a reflector, a flat, orotherwise shaped, reflector may increase the effective capture area ofreflected light.

FIG. 21 provides a cross-sectional view of a reflector 2180 includingoptical elements for reflecting light. In certain embodiments, thereflector 2180 is a vertical reflective prismatic panel. One or moresurfaces, or portions of one or more surfaces, of the reflector 2180 maybe angled with respect to the plane of the reflector 2180. For example,a back surface 2156 of reflector 2180 may comprise one or more angledsurface regions 2156 a, 2156 b, that are angularly offset with respectto the plane of the reflector 1280 by an angle θ₃ (e.g., 5°, as shown inFIG. 21). The surface 2156 may be reflective, such that direct lightL_(D) striking the surface is reflected towards a light capture target.Similarly to the effect of tilting the reflector, as described abovewith respect to FIG. 17, providing an angled surface 2156 a, 2156 b willgenerally change the resultant solar altitude or reflected light L_(R)10 degrees for every 5 degree angular offset with respect to the planeof the reflector, whether the offset is negative or positive.Specifically, in the embodiment of FIG. 21, the angle θ₂ of reflectedlight L_(R) with respect to a horizontal plane is 10° greater than theangle θ₁ of direct light L^(D), where the light reflector 2180 has agenerally vertical orientation. The surface 2156 may include one or moretapering regions 2157 to allow for multiple angled sections 2156 a, 2156b while maintaining a reflector 2180 thickness within a desired range.

In certain embodiments, the reflector 2180 comprises a transparentpolymer, with a surface, such as surface 2156, being reflective. Forexample, surface 2156 may be rendered reflective by a vapor coating(e.g., aluminum, silver, etc.). Incorporating one or more opticalelements into a reflector, such as by fabricate a prism in a clearmaterial that has that slope, may serve as an alternative toreflector-tilting, or may be combined with reflector-tilting techniquesin order to enhance the turning capabilities of the reflector. Incertain embodiments, incorporating one or more reflective prisms in areflector allows for maintenance of a reflective panel in a verticalorientation, with the reflective prism being configured to change thebisected angle.

In certain embodiments, a parabolic reflector comprises one or moreoptical elements that are designed to compensate for the distance to alight collector as you proceed further away from the vertex of theparabola. For example, a reflective panel may be flat (e.g., no prism)at or near the vertex, and increase in angle as you get closer to therim angle, either continuously, or in discrete increments. This mayallow for reduced height of the reflective panel to cover the height ofthe collector. With reference to FIG. 13, in certain embodiments, aparabolic reflector having a focal point p approximately 9 inches fromthe vertex v of the parabola is positioned approximately 1.2 inches fromthe outer surface of a light collector 1220 at the vertex v, but may beas far as 17.5 inches or more from the light collector at certainpositions at the peripheral portions 1283 of the reflector (e.g., for aparabolic reflector 1280 having a 48-inch aperture 1281. Therefore, iflight is reflected downward at, for example, 30 degrees, it may strikethe light collector at a point approximately 0.7 inches below thereflected point at the vertex v, but greater than 10 inches below thereflected point at certain peripheral portions 1283.

In certain embodiments, prismatic element facing the direction of directlight L_(D) bends the light prior to reflection by a reflective surface.In such embodiments, the reflective surface may be substantially planar,or may include one or more angularly offset portions. Furthermore, areflector in accordance with embodiments disclosed herein may includeany suitable alternative optical elements in addition to, or in placeof, those optical elements discussed above.

FIG. 22 provides a perspective view of a sunlight collection system 2200in accordance with principles discussed herein. System 2200 includes alight collector 2220 and a reflector 2280. FIG. 23 provides an explodedview of the reflector 2280 and light collector 2220 of the system 2200.Prismatic film 2348 is nestingly disposed within light collector 2220.Prismatic films that may be similar to that shown in FIG. 23 arediscussed above in connection with FIG. 6.

The sunlight intensity on the reflector 2280 will depend on, among otherthings, the incident angle of the sunlight with respect to the face ofthe reflector 2280. As an example, if light with an intensity of 1,000lumens reflects off a reflective panel with an incident angle of 30degrees, the intensity per area may be reduced to approximately 866lumens (1,000×))cos(30°. Generally, the smaller the incident angle, thehigher the light density. Table K provides calculated light intensityvalues for a reflector surface with respect to sunlight at incrementalaltitudes between 20 and 70 degrees. The table provides reflective panellight intensity values with respect to varying tilt angles of thereflector panel.

TABLE K Reflective Panel Light Intensity (100% is maximum) Tilt TiltTilt Tilt Solar Tilt 25° Tilt 20° Tilt 15° Tilt 10° Tilt 5° Tilt 5° 10°15° 20° 25° Altitude Forward Forward Forward Forward Forward VerticalBack Back Back Back Back (degrees) (%) (%) (%) (%) (%) (%) (%) (%) (%)(%) (%) 20 71 77 82 87 91 94 97 98 100 100 100 30 57 64 71 77 82 87 9194 96 98 100 40 42 50 57 64 71 77 82 87 91 94 96 50 26 34 42 50 57 64 7177 82 87 91 60 9 17 26 34 42 50 57 64 71 77 82 70 — — 9 17 26 34 42 5057 64 71

It may be desirable for light from the reflector to enter the collectorassembly at a solar altitude of approximately 30 to 40 degrees in orderfor the optics of the collector assembly to be utilized effectively.Therefore, as demonstrated by Table K, in the presence of sunlighthaving a solar altitude of 60 degrees, it may be desirable to tilt thereflector back 15 to 20 degrees in order to reduce the solar altitudedown to 30 or 40 degrees. On the other hand, in the presence of sunlighthaving a solar altitude of 20 degrees, it may be desirable to tilt thereflector forward 5 to 10 degrees to accomplish the same result.

It should be noted that tilting the reflective panel forward may changethe resultant angle of reflection 10 degrees for every 5 degree paneltilt from vertical, while tilting the panel back from vertical maydecrease the resultant angle of reflection by the same ratio. Asunlight-collection assembly comprising a reflective panel can beconfigured such that any desired angle of reflection (such as, forexample, 20 degrees) is maintained.

With further reference to FIG. 12, in order to maintain the vertex ofthe parabola substantially in line with a vertical plane of the solarazimuth angle, it may be desirable for the reflector 1280 to rotatearound the collector assembly 1220. For example, the reflector mayrotate around the collector at approximately the same rate as theazimuth movement of the sun, within a certain degree of tolerance.Reflective or refractive concentrators that focus sunlight directly intoan opening often require less than a degree of tracking error in orderto maintain performance. In certain embodiments, the use of a continuouslarge target (e.g., the width of a collector 1220) may allow for asubstantial error without losing substantial focus and associatedperformance. The following table illustrates the reduction inperformance versus azimuth tracking error with respect to certainembodiment TDD systems comprising a collector target having asubstantially vertical light collection surface:

TABLE L Azimuth Tracking Error Performance Reduction (degrees) SystemPerformance From 0 degrees 0 100% — 5 88% 12% 10 83% 17% 15 70% 30% 2055% 45% 25 42% 58%

As shown in Table L, in certain embodiments, the refractive lenses ofthe collector assembly are configured to direct light into a daylightingaperture at incident angles off axis within a certain range (e.g.,approximately +/−5 degrees). Designing and fabricating a trackingmechanism that can operate with an error of +/−5 degrees may besignificantly easier and/or less costly than tracking mechanismsrequiring accuracy within, for example, a single degree. It also may beadvantageous to operate a system that may maintain a 50% performancelevel with an error of greater than 20 degrees, as shown in Table L.

Table M provides the calculated effective area of a clear dome sunlightcollection system without a parabolic reflective panel, as compared tothe effective areas of example cylindrical collector assemblies andclear dome assemblies with reflector panels, at various solar altitudesand reflector panel tilt angles.

TABLE M Clear Dome/No Solar Cylinder-Dome System Clear Dome System Ref.Panel Altitude (panel tilt/ (panel tilt/ (effective (degrees) systemeffective area) system effective area) area) 20 vertical/487.8 in² 25°fwd/226.8 in²  49.7 in² 30  5° back/471.2 in² 20° fwd/232.5 in²  72.6in² 40 10° back/450.9 in² 15° fwd/235.3 in²  93.3 in² 50 15° back/420.5in² 10° fwd/236.8 in² 111.2 in² 60 20° back/387.3 in²  5° fwd/231.3 in²125.7 in² 70 25° back/346.8 in² vertical/221.5 in² 136.4 in²

The data presented above demonstrates the potential performance ofsunlight-collection systems incorporating reflective panels. As shown inTable M, the effective collection area from the parabolic reflector witha cylindrical collector assembly may be more than 300% greater than thatof a horizontal tube opening without a reflector for certain solarangles. Furthermore, a collector assembly may provide a near constantillumination level over extended periods of the day due to the increasedcollection area at low solar angles when sunlight intensity levels arereduced and lower collection areas at high solar angles when sunlightintensity levels are higher.

As demonstrated, a clear dome system comprising a reflective panel mayhave a reduced effective collection area when compared to a cylindricalcollector assembly due to reduced reflector collection of sunlight. Thismay occur due to higher incident angles of the sun to the reflectorpanel plane required to reflect light down to a horizontal opening. Thearea of the horizontal aperture may also be a limiting parameter whencompared to a larger vertical capture area of a cylindrical collectorassembly.

A series of computer models can be used to test the amount of lightdirected into a horizontal tube opening in a system incorporating aparabolic reflector. The tests could include comparisons of theperformance of two parabolic reflector system designs, one using acylinder-dome light collector, and the other using a conventional cleardome, and a system comprising a conventional clear dome without areflector. The dimensions and other parameters are provided in Table N:

TABLE N Parabolic Reflector System w/Prismatic Parabolic Reflector ClearConfiguration Cylinder Dome w/Clear Dome Dome Tube Diameter 21″ 21″ 21″Parabolic Reflector 70.8″/13.3″ 70.8″/13.3″ — Aperture/Vertex ParabolicReflector 36″ 36″ — Height Ref./Dome 212° 212° — Circumference CoverageCylinder 14.2″/23″   14.2″/23″   — Height/Diameter Dome/Lens film 8″/6″8″/6″ — Height

Using the above design specifications and associated optics of collectorlenses, transmission/reflection of the materials, and geometries,collimated light patterned after sunlight can be projected onto thesystem at solar elevations ranging from 20 degrees to 70 degrees in 10degree increments. The intensity of the light for each solar elevationcan be varied based on Illuminating Engineering Society of North America(“IES”) Standards for Direct Insolation. The results do not take intoaccount the diffuse content. The results are listed in Table O.

TABLE O Parabolic Parabolic Reflector Reflector w/ Cylindrical SolarAltitude Clear Dome w/ Clear Dome Collector (Degrees from (units ofluminous (units of luminous (units of luminous horizontal) flux) flux)flux) 20  1.0 units  9.43 units 11.03 units 30 1.77 units 12.24 units14.75 units 40 2.50 units 13.43 units 16.42 units 50 3.15 units 14.23units 16.24 units 60 3.67 units 14.52 units 15.52 units 70 4.06 units14.61 units 13.84 units

Table P provides a comparison of the computer simulated ratios of theclear dome to the parabolic reflector with cylindrical collector (TableN) to the same ratios from the analysis above of the effective sunlightcollection areas (Table L). This fraction may be considered the opticalefficiency of the dome.

TABLE P Cylinder Dome Optical Effective Area Computer SimulatedEfficiency Solar Altitude Ratios Performance Results (comp. sim.(Degrees from (cyl.-dome/clear Ratios (cyl.-dome/ ratios/ horizontal)dome) clear dome) eff. area ratio) 20 9.45 11.03 117% 30 6.35 8.31 131%40 4.69 6.56 140% 50 3.65 5.16 141% 60 2.96 4.24 143% 70 2.44 3.41 140%

As shown in Table P, for each of the incremental solar altitudemeasurements, the efficiency is greater than 100%. At a maximum, theexpected results should not have exceeded 100% efficiency. Therefore,the principles disclosed herein yield far greater performance andresults than expected or anticipated—up to 143% greater. These resultsmay be an indication that the effective light capture area analysisperformed above does not fully represent the performance-increasingeffect that the addition of a reflector as disclosed herein may have ona daylight-collection system. The greater than 100% efficiency values inTable O may be attributable to one or more unknown or unforeseeablefactors. For example, the unexpected performance may be due to anincrease in the reflected light altitude angle from the periphery of thereflector. For example, if a parabolic reflector is vertical, any lightreflecting at the center or vertex of the parabola may reflect at thesame incident angle. There is an additional turning angle at positionsaway from the center of the reflector due to the curvature of thereflector, which may increase the reflected angle by a cosine functionof the turning angle.

Discussion of the various embodiments disclosed herein has generallyfollowed the embodiments illustrated in the figures. However, it iscontemplated that the particular features, assemblies, orcharacteristics of any embodiments discussed herein may be combined inany suitable manner in one or more separate embodiments not expresslyillustrated or described. For example, it is understood that anauxiliary light fixture can include multiple light sources, lamps,and/or light control surfaces. It is further understood that theauxiliary lighting fixtures disclosed herein may be used in at leastsome daylighting systems and/or other lighting installations besidesTDDs.

It should be appreciated that in the above description of embodiments,various features are sometimes grouped together in a single embodiment,figure, or description thereof for the purpose of streamlining thedisclosure and aiding in the understanding of one or more of the variousinventive aspects. This method of disclosure, however, is not to beinterpreted as reflecting an intention that any claim require morefeatures than are expressly recited in that claim. Moreover, anycomponents, features, or steps illustrated and/or described in aparticular embodiment herein can be applied to or used with any otherembodiment(s). Thus, it is intended that the scope of the inventionsherein disclosed should not be limited by the particular embodimentsdescribed above, but should be determined only by a fair reading of theclaims that follow.

1. (canceled)
 2. A daylighting apparatus configured to direct naturaldaylight into an interior of a building, the apparatus comprising: an atleast partially transparent light-collecting assembly comprising asidewall portion and a collector base aperture; a light turning assemblycomprising at least one prismatic element, the at least one prismaticelement positioned and configured to turn light transmitted through theat least partially transparent light-collecting assembly towards thecollector base aperture; and a reflector positioned and configured toreflect daylight towards the sidewall portion, wherein the reflector ispositioned outside the light-collecting assembly; wherein thedaylighting apparatus is configured to provide daylight to the interiorof the building when the daylighting apparatus is installed on a roof ofthe building.
 3. The daylighting apparatus of claim 2, wherein thereflector comprises one or more optical elements configured to alter anangle of reflection of at least a portion of light that strikes thereflector.
 4. The daylighting apparatus of claim 3, wherein the one ormore optical elements comprise a prismatic element.
 5. The daylightingapparatus of claim 4, wherein the reflector comprises a first portionhaving a first prismatic element, and a second portion having a secondprismatic element, wherein the first prismatic element and secondprismatic element have different light-turning characteristics.
 6. Thedaylighting apparatus of claim 2, wherein the reflector is curved in oneor more dimensions.
 7. The daylighting apparatus of claim 2, wherein thereflector comprises a plurality of segments.
 8. The daylightingapparatus of claim 2, wherein the reflector is substantiallyparabolically-shaped along at least one axis of curvature.
 9. Thedaylighting apparatus of claim 8, wherein a cross-sectional center ofthe light-collecting assembly is positioned at a focus point of theparabolically-shaped reflector.
 10. The daylighting apparatus of claim2, wherein the reflector is configured to automatically reposition togenerally track a solar azimuth angle.
 11. The daylighting apparatus ofclaim 10, wherein the reflector is further configured to automaticallyreposition to generally track an elevation of the sun.
 12. Thedaylighting apparatus of claim 2, wherein the light-collecting assemblycomprises a top cover portion.
 13. The daylighting apparatus of claim12, wherein the at least one prismatic element is disposed within atleast one of the sidewall portion or the top cover portion.
 14. Thedaylighting apparatus of claim 13, wherein the at least one prismaticelement comprises a prismatic film.
 15. The daylighting apparatus ofclaim 12, wherein the at least one prismatic element is molded into atleast one of the sidewall portion or the top cover portion.
 16. Thedaylighting apparatus of claim 2, wherein the at least one prismaticelement comprises a prismatic film and disposed within the sidewallportion of the light-collecting assembly.
 17. A method of providinglight to an interior of a building, the method comprising: positioning areflector outside of a light-collecting apparatus, the light collectingapparatus positioned over a daylighting aperture formed in a buildingenvelope; reflecting daylight using the reflector towards thelight-collecting apparatus; transmitting the reflected daylight throughan at least partially transparent sidewall of the light-collectingapparatus; and turning the reflected natural daylight towards thedaylighting aperture using at least one prismatic element disposedwithin the light collecting apparatus such that a portion of thereflected daylight is available for illuminating the interior of thebuilding.
 18. The method of claim 17, further comprising automaticallyrepositioning the reflector such that an apex of the reflector generallytracks a solar azimuth angle.
 19. The method of claim 18, whereinautomatically repositioning the reflector includes repositioning togenerally track an elevation of the sun.
 20. A daylighting apparatus forproviding daylight to the interior of a building, the apparatuscomprising: a daylight collector comprising a sidewall portion and adaylighting aperture configured to be positioned on a roof of thebuilding when the daylighting apparatus is installed on the building; areflector having a substantially parabolic shape, the reflectorconfigured to reflect daylight toward the daylight collector, thereflector positioned outside of daylighting aperture; and a lightturning prismatic element configured to turn reflected daylighttransmitted through the daylight collector towards the daylightingaperture.
 21. The apparatus of claim 19, further comprising a trackingsystem configured to turn the reflector such that an apex of thereflector generally tracks a solar azimuth angle during daylight hours.22. The apparatus of claim 19, wherein the reflector has a luminousreflectance greater than or equal to about 95% when measured withrespect to CIE Illuminant D₆₅.
 23. The apparatus of claim 19, whereinthe light turning optical element comprises a prismatic film positionedto refract light passing through the daylight collector.
 24. Theapparatus of claim 19, wherein the light turning optical elementcomprises a reflector positioned to reflect light passing through thedaylight collector.
 25. The apparatus of claim 19, wherein the reflectoris configured to tilt forward and/or backward.